Edexcel Physics Unit 4 20th Jan Watch

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jtaylor
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Who is sitting this paper tomorrow?
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Weirdo
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I'm sitting unit 4 tomorrow unfortunately...

what time do you guys start the exam in England? I'll be finished by 11:15 (7:15 UK time)...
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Worried
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Not Edexcel, but I'm sitting the OCR one tomorrow.
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Weirdo
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I didn't like the exam at all! the first question put me off completely... I know I can resit it, but I already have 15 exams to sit in May/June!

Anyway, how did everyone else find it?
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The Best
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(Original post by Weirdo)
I didn't like the exam at all! the first question put me off completely... I know I can resit it, but I already have 15 exams to sit in May/June!

Anyway, how did everyone else find it?
Im just bac. from the edexcel Phys4. Well, typical physics exam. The calculation in the 1st ques for 4 marks was a nightmare. I got 205 m/s but im sure its wrong. Then the question fot 7 marks of the resonance and natural frequency etc... was also difficult. I didn't know what to draw or write down! What i did was drew the apparatus for producing a standing wave (signal generator, vibrator etc...) but im not quite sure if it's related to the ques!!!!!!!!

In the SHM ques, where it asked to find the frequency what did u get?

Anyone remember their answers?
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emporium
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(Original post by The Best)
Im just bac. from the edexcel Phys4. Well, typical physics exam. The calculation in the 1st ques for 4 marks was a nightmare. I got 205 m/s but im sure its wrong. Then the question fot 7 marks of the resonance and natural frequency etc... was also difficult. I didn't know what to draw or write down! What i did was drew the apparatus for producing a standing wave (signal generator, vibrator etc...) but im not quite sure if it's related to the ques!!!!!!!!

In the SHM ques, where it asked to find the frequency what did u get?

Anyone remember their answers?
Yep, the first question was definately one of the most badly worded / set out questions I've ever seen, I reckon over half the marks I've dropped are on Q1, gah!!
The rest seemed to be reasonable, luckily I remembred the mass on spring forced vibrations experiment heh.
For the frequency I got something like 2.7 Hz, around that figure, 20 cycles divided by 7.something seconds whatever it was.
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Resonance
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Hi

I just got back from doing that exam. I found that first question very tough. I need an A and I think Question 1 in total is worth 11 marks, out of which I probably got 1, so I think I'll be resitting that for sure, like you Weirdo I have loads of exams then too.

What did you put down as the reason for the maxima and minima on the first question? Like a fool I put it down to diffraction, but I looked in the Nelson textbook and it shows that it's meant to show stationary sound waves!

For the frequency of the SHM question I got something around 2.6Hz. I thought that resonance experiment one was ok, and as for the one about the car flying off the hill, my teacher had studied that situation with us many times and even though I botched it to begin with I think I will get decent marks for it.

But overall that hasn't done much for my confidence, which is not good because I have AQA CHM4 tomorrow.
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jtaylor
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The first question was a killer one. I had absolutely no idea what so ever.Well, i guess i kinda got it as i talked about stationary waves and stuff, but 5 marks!!!! As for the second one, I got a value of about 1/2 the speed of sound (about 170m/s). I thought about doubling it was it would be logical but in the end i just left it. My freind told me when he got got of the exam that the value had to be mutliplied by 2 was it was between 2 nodes and the wavelength is between 3. However, being an ossciloscope you would assume the the wavelength on it is the actual wavelength, not the distance between 2 nodes.
Overall I think that i found the exam relatively easy and apart from question 1 which i think everybody screwed up i shoul do fine. Hopefully the grade boundries will be lowered because of that question. Wha did you guys put for the final part of question 1?
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emporium
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(Original post by jtaylor)
The first question was a killer one. I had absolutely no idea what so ever.Well, i guess i kinda got it as i talked about stationary waves and stuff, but 5 marks!!!! As for the second one, I got a value of about 1/2 the speed of sound (about 170m/s). I thought about doubling it was it would be logical but in the end i just left it. My freind told me when he got got of the exam that the value had to be mutliplied by 2 was it was between 2 nodes and the wavelength is between 3. However, being an ossciloscope you would assume the the wavelength on it is the actual wavelength, not the distance between 2 nodes.
Overall I think that i found the exam relatively easy and apart from question 1 which i think everybody screwed up i shoul do fine. Hopefully the grade boundries will be lowered because of that question. Wha did you guys put for the final part of question 1?
Taylor, sounds like you at least talked about the right topic for the 5 marker; stationary waves, I didn't even mention them heh The examiners deserve a slap for that question, I don't mind admitting when Im just too stupid to answer a question, but that was just poor, there should have been a better indication of what they were looking for, and I agree about the oscilloscpe, the whole thing was very confusing I thought. For the final part I said that the area over which the waves are spread increases as the speaker is taken further away therefore the Intensity decreases, so the amplitude displayed on the oscilloscope decreases.
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Emma Louise
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I did this paper this morning as well. Got 2.63Hz for that frequency bit like someone else said. For the speed of sound I got 160m/s. The past papers have been a lot easier though!

"For the final part I said that the area over which the waves are spread increases as the microphone is taken further away therefore the Intensity decreases, so the amplitude displayed on the oscilloscope decreases."

I put that, about the inverse square law, then crossed it out and put something else. Nightmare.
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emporium
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(Original post by Emma Louise)
I did this paper this morning as well. Got 2.63Hz for that frequency bit like someone else said. For the speed of sound I got 160m/s. The past papers have been a lot easier though!

"For the final part I said that the area over which the waves are spread increases as the microphone is taken further away therefore the Intensity decreases, so the amplitude displayed on the oscilloscope decreases."

I put that, about the inverse square law, then crossed it out and put something else. Nightmare.
lol, you probably put the right answer, I havn't got a clue what the actual answer was, not sure what the mysterious mind of the edexcel physics examiner was after.....
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Resonance
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For the final part of Q1, I put down something about intensity. I mentioned the inverse square law. But that will probably not be enough to salvage the debacle that was whatever I wrote down for part a).
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The Best
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What did u guys write for the Resonance experiment question for 7 marks? I'm really worried coz i messed it up soooo much :mad:

I really hate those physics exams... i do hope they higher the marks!
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jtaylor
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yeh, 7 marks!
I thought that it was really tough to get all 7. I think that there is 4 marks for an accurate diagram and explanation of its use (I used a spring and frequency generator to measure the maximum amplitude and frequency) and 1 mark per accurate definition for the 3 terms. Overall though, i just explained how to carry out the experiment to get the values and described the terms.
Lets write out all the answers we can remember so that we can check.
Q2) F=mv^2/r and acting towards the centre of the circle
F(when stationary)=mg=925 times 9.81
= 9074N
F (moving) = 3700N
Critical speed = 15.7m/s
Apparent weightlessness = falling free at rate of 'g', body not under any other forces accept gravitational attraction and thus fell weightless.

Q3) S.H.M
'a' proportional '-x'
a=acceleration
-x=displacement in opposite direction

x=0.036m
v=2.63Hz
x=-0.026m

Q4) resonance exp.
Q5).......cannot really remember up to Q7
Q8) Redshift is the relative movement of one object to another so that the wavelength appears to shift towards the red end of the spectrum adn thus becomes longer.
The change in wavelength is evidence that the universe is expanding as all the galaxies appear red shifted.
Mistakes and blanks, plz fill in
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mathematician
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q2. 9074 - 3700 was the answer,
i put 3700N but its wrong, its the resultant u want,
for the first question u had to mention about maxima at the anti nodes and minima at the nodes, due to the super position of the waves reflected from the bench, the second part was 340m/s
because that amplitude displacement graph was of a stationary wave!.
so u had to find the distance between to node, anti nodes and multiply it by 2.
for the last part of one u had to mention intensity of the wave.
SHM question was easy, but for the last part of it where u had to talk about y its a bad equation, was because the oscilations dies away, e.g energy is lost to surroundings.
and for the very last question u had to say because of red shifting it suggests tht galaxies r moving away, so we live in an expanding universe.
they were the tricky ones.
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acidbubble
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i did the edexcel B module 4 one this morning, it seems simple in comparison to the stuff u lot r on about :P
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Resonance
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For the big ol' 7 mark resonance experiment question, I drew a diagram of Frequency generator connected to motor-driven oscillator connected to string to pulley to spring-mass system.

Then I said make the motor thingy oscillate, and it will force the spring to oscillate at the same frequency, hence forced oscillations. amplitude will be small. then increase the frequency of the motor until you get big amplitude oscillations from the spring-mass system. At this point resonance is occuring. if you increase frequency further the amplitude of the spring-mass drops because it is no longer at its natural frequency.

For the car on the hill question, I said that R = mg when it's standing still.

Then when it's moving at 10ms-1 or something, Fc = mg - R, so R = mg - Fc = mg - mv²/r.

Then for the critical speed i rearranged that to get v = (root)rg which was 15.something, I think. I had a bit of trouble explaining why the car 'takes off'. But I said that free-fall is when only force on you is mg, and so no contact forces so no tensions and compressions that they would produce, so you are in a state of apparent weightlessness.

And that red-shift thing, I think I got it down but I didn't articulate it brilliantly.
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rhino
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(Original post by jtaylor)
yeh, 7 marks!
I thought that it was really tough to get all 7. I think that there is 4 marks for an accurate diagram and explanation of its use (I used a spring and frequency generator to measure the maximum amplitude and frequency) and 1 mark per accurate definition for the 3 terms. Overall though, i just explained how to carry out the experiment to get the values and described the terms.
Lets write out all the answers we can remember so that we can check.
Q2) F=mv^2/r and acting towards the centre of the circle
F(when stationary)=mg=925 times 9.81
= 9074N
F (moving) = 3700N
Critical speed = 15.7m/s
Apparent weightlessness = falling free at rate of 'g', body not under any other forces accept gravitational attraction and thus fell weightless.

Q3) S.H.M
'a' proportional '-x'
a=acceleration
-x=displacement in opposite direction

x=0.036m
v=2.63Hz
x=-0.026m

Q4) resonance exp.
Q5).......cannot really remember up to Q7
Q8) Redshift is the relative movement of one object to another so that the wavelength appears to shift towards the red end of the spectrum adn thus becomes longer.
The change in wavelength is evidence that the universe is expanding as all the galaxies appear red shifted.
Mistakes and blanks, plz fill in

How did u get F moving = 3700N (It was moving at 10 ms) when F stationary = 9074??
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SasunD
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i think that i messed up the question about the car, kos i put (when moving) R = mg + Fc. i couldnt get a good critical speed as it was too great.

You know the question about moving the microphone, did it say moving it closer to the sources, kos i remember it saying moving further away from the table. taking the latter as the question, i wrote that as you get closer to the mic, the waves coming out are all together and moving apart, so they are interferring with each other as the distance between the waves is not at least one wavelenght apart...

for the resonance one, i put, you get an empty wine glass, flick it and record the frequency of the sound created, using a mic connected to oscilliscope. then you put a speaker next to the wine glass and plug a sound generator into the speaker. you make the generator play a sound of nearly same natural freq as glass, and the glass vibrates/osciallates. then play sound of natural freq and the glass shatters.

but yeah, i found the car the hardest one as we hadn't gone over a question quite like that. the closet one i can rememebr is spinning a bung on a string in a vertical circle, where the tension in the string changes depending on location in cycle....
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MalaysianDude
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How did u get F moving = 3700N (It was moving at 10 ms) when F stationary = 9074??
just use R = mg - mv²/r
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